The Belfast light-fly, who has claimed three wins in Guwahati so far this week, beat 2015 World Junior bronze medalist Karina Tuvakova of Russia via split decision.
The Mac Lady, a European silver medalist earlier this year, will now box Ukrainian Zhazira Urakbayeva in the semi finals at the weekend.
Earlier today Kildare light welter Katelynn Phelan claimed bronze with a win over American Aidyl Cardenas.
However there was disappointment for Bray welter Shannon Reilly who lost out to Citalli Ortiz of the USA.
Irish team manager Anna Moore described the performances of the Irish trio as magnificent.
Tomorrow is a rest day at the tournament with the semi-finals due to be decided on Friday (Phelan) and Saturday (Fryers). The finals will be held Sunday.
AIBA Youth Women’s World Boxing Championships Guwahati, India
51kg Shauna Blaney (Ireland) lost to Ekaterina Molchanova (Russia) 0-5
48kg Caitlin Fryers (Ireland) beat Nasu Misaki (Japan) 5-0
69kg Shannon Reilly (Ireland) beat Olivia Hussey (England) 3-2
75kg Lauren Kelly (Ireland) lost to Ya Chun-Yang (Taiwan) 0-5
48kg Caitlin Fryers (Ireland) beat Sumaiya Kosimova (Tajikistan) 5-0
54kg Mary Geraghty (Ireland) lost to Marie Bachmaier (Germany) 1-4
57kg Labhaoise Clarke (Ireland) lost to Namuun Monkhor (Mongolia) RETI3
60kg Marguerita Nevin (Ireland) lost to Klaudia Budasz (Poland) 2-3
48kg Caitlin Fryers (Ireland) beat Karina Tuvakova (Russia) split
64kg Katelynn Phelan (Ireland) beat Aidyl Cardenas (USA) 4-1
69kg Shannon Reilly (Ireland) lost to Citalli Ortiz (USA) Pts
64kg Katelynn Phelan (Ireland) v Ekaterina Dynnik (Russia)
48kg Caitlin Fryers (Ireland) v Zhazira Urakbayeva (Ukraine)
48kg Caitlin Fryers (Immaculata) (Bronze, at least)
51kg Shauna Blaney (Navan)
54kg Mary Geraghty (Baldoyle)
57kg Labhaoise Clarke (Carndonagh)
60kg Marguerita Nevin (St.Brigid’s, Kildare)
64kg Katelynn Phelan (St.Brigid’s, Kildare) (Bronze, at least)
69kg Shannon Reilly (Bray)
75kg Lauren Kelly (St.Brigid’s, Edenderry)
Team manager: Anna Moore
Coaches: Jimmy Payne, Liam Brereton, Antia Just
R&J: Sadie Duffy